Cellular Glass Insulation

Cellular glass, also called foam glass, is rigid insulation made by heating crushed or recycled glass with a foaming agent such as carbon or limestone. Gas released during heating forms bubbles, and the cooled product is a block of glass whose volume is mostly sealed cells. Saint-Gobain filed the first patent for foam glass made with calcium carbonate in 1932; the Foamglas product was later developed by Pittsburgh Corning.

Properties

• Closed cells: more than 75% of the insulating product consists of closed cells, so it has no capillary action and does not absorb water.
• Vapour: the glass cell walls make boards effectively vapour-tight; a fully bonded cellular glass layer can act as its own vapour control.
• Strength: rigid and dimensionally stable, suited to heavy loads.
• Fire: made of glass, so non-combustible; one major product is classed Euroclass A1.
• Durability: resistant to rot, pests and most chemicals.

Thermal conductivity of cellular glass boards is higher than that of polyiso or XPS, so more thickness is needed for the same thermal value. Loose foam-glass aggregate, used as fill, has a lambda of about 0.08 W/(m.K).

Roof uses

Cellular glass is chosen for compact (fully bonded) warm roofs, particularly in central Europe, where boards are set in hot bitumen on concrete or steel decks so that no water can travel within the assembly. It is also used under green roofs, parking decks, plazas and roofs with heavy plant, and for tapered schemes.

Considerations

Boards are brittle and must be handled carefully; surfaces exposed to traffic during construction need protection. Cost is usually higher than foam insulations.

Approvals

Compact cellular glass roof assemblies have been tested as complete systems; one manufacturer offers an FM Approved compact roof system for demanding commercial roofs and separate systems for trafficked activity roofs.